Embodiments of the invention relate generally to power semiconductor converters, and more particularly to measuring the current in thyristors and balancing the current load on thyristor bridge circuits.
In this regard, thyristor bridge circuits connected in parallel include legs. A leg is a group of thyristors wherein each thyristor of the leg occupies a similar position in a thyristor bridge circuit. In operation, each thyristor in a leg is often gated at the same time.
When the thyristors in a leg are gated at the same time, there may be a current load imbalance between the thyristors in the leg. One reason for the current imbalance may, for example, be caused by the geometric differences among each thyristor in the leg. For example, one thyristor of a leg may have contact points closer to a power bus than another thyristor in the leg resulting in a current imbalance once the leg is gated. A current imbalance may increase the heating of an individual thyristor that may cause the thyristor to fail prematurely.
Thus, it is desirable to use an apparatus and method for controlling a thyristor bridge circuit that allows each thyristor in a leg to share a substantially equal distribution of the current load when the thyristors in the leg are gated.